A power transmission component, such as a clutch or a propeller shaft, receives varying torque about a rotation axis in a state where the power transmission component rotates at a high speed. In order to accurately evaluate the fatigue resistance of such a component, a rotational torsion test where torque (a torsion load) is applied to a test piece about the rotation axis while rotating the test piece is performed.
Japanese Patent Provisional Publication No. 2004-125549A (hereafter, referred to as patent document 1) discloses a rotational torsion tester including a hydraulic actuator 52 which applies torque to a test piece 11, and an AC motor 58 which rotates the hydraulic actuator 52 and the test piece 11 in a synchronized manner. The AC motor 58 rotates a main body of the hydraulic actuator 52, and rotates an output shaft of the test piece 11 coaxially at the same speed as that of the main body of the hydraulic actuator 52. An output shaft of the hydraulic actuator 52 is coupled to an input shaft of the test piece 11, so that, by driving the AC motor 58 and the hydraulic actuator 52, torque can be applied to the test piece 11 while rotating the test piece 11. The torque applied to the test piece 11 is measured by a torque detector 47 provided between the output shaft 46 and the test piece 11.